<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title> </title>
    <script src="js/vue.min.js"></script>
</head>
<body>
<div id="app">
    <input type="text" v-model="n1">
    <select name="" id="" v-model="opt">
        <option value="+">+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
        <option value="%">%</option>
    </select>
    <input type="text" v-model="n2">
    <input type="button" value="=" @click="calc">
    <input type="text" v-model="result">
</div>
<script>
    var vm=new Vue({
        el:'#app',
        data:{
            n1:0,
            n2:0,
            result:0,
            opt:'*'
        },
        methods:{
            calc(){
                // switch (this.opt) {
                //     case "*":this.result=parseFloat(this.n1)*parseFloat(this.n2); break
                //     case "/":this.result=parseFloat(this.n1)/parseFloat(this.n2); break
                //     case "+":this.result=parseFloat(this.n1)+parseFloat(this.n2); break
                //     case "-":this.result=parseFloat(this.n1)-parseFloat(this.n2); break
                //     case "%":this.result=parseFloat(this.n1)%parseFloat(this.n2); break
                // }
                var  codeStr='parseFloat(this.n1)'+this.opt+'parseFloat(this.n2)'
                this.result=eval(codeStr)
            }
        }
    })
</script>
</body>
</html>